1. Field of the Invention
The present invention relates to an image reading apparatus and, more particularly, to an image reading apparatus for reading a light-transmission original such as a film by using a contact image sensor and an area light source used for the image reading apparatus.
2. Description of the Related Art
An image sensor for reading an original is used for image reading apparatuses such as a facsimile machine and a copy machine. The image sensor includes a reduction-type image sensor used for reduction-optical-system-type image reading apparatuses and a contact image sensor used for contact unity-magnification-optical-system-type image reading apparatuses. The contact image sensor comprises a light source, an erect unity-magnification imaging optical system, a sensor, etc. As compared with the reduction-type image sensor, generally, this contact image sensor has such a merit that a light-path length is shorter, the size of equipment is compact, its troublesome optical adjustment is improved, and it is easily assembled in equipment. In place of the reduction-type image sensor, the contact image sensor is variously used.
FIG. 1 shows a reduction-optical-system-type image reading apparatus using a white light source and a sensor with color filters. In a case 18, the image reading apparatus in FIG. 1 includes a fluorescent lamp light source 10, a mirror 12, a lens 14, and a CCD sensor 16 with color filters. An upper surface of the case 18 is an original plate glass 20 onto which a sheet original 22 is placed and is pressed by an original cover 24. The fluorescent lamp light source 10 and the mirror 12 are reciprocatedly driven in a predetermined direction, thereby reading and scanning the original. Light 15 outputted from the fluorescent lamp light source 10 is reflected to the sheet original 22 and is inputted to the CCD sensor 16 with the color filters via the mirror 12 and the lens 14.
Further, the reduction-optical-system-type image reading apparatus comprises an area light source, serving as a light source for transmission, for reading an image of a light-transmission original such as a negative/positive film (hereinafter, simply referred to a film original). FIG. 2A shows the reduction-optical-system-type image reading apparatus, comprising the area light source. Referring to FIG. 2A, an area light source 28 is provided on a film original 26. Referring to FIG. 2B, the area light source 28 comprises a fluorescent lamp 32 on three sides of a rectangular light guide plate 30. The area light source 28 is incorporated in an original cover (not shown) or is replaced with the original cover when the film original is read.
When a film is read, the fluorescent lamp light source 10 is lit off and the area light source 28 is lit on. Light outputted from the area light source 28 passes through the film original 26, the mirror which is reciprocatedly driven for reading and scanning the film, and the lens 14, and is inputted to the CCD sensor 16 with the color filters.
FIG. 3 shows a contact-unity-magnification-optical-system-type image reading apparatus, using a light source 34 of red (R), green (G), and blue (B) light, which can be lit on by a switching operation, and a line sensor without filters. In the contact-unity-magnification-optical-system-type image reading apparatus, a contact image sensor 36 is provided in the case 18 and an upper surface thereof is an original plate glass 20 on which a sheet original 22 is placed and is pressed by an original cover 24.
The contact image sensor 36 is reciprocatedly driven in a predetermined direction, thereby reading and scanning an original. Light outputted from the light source 34 is reflected to the sheet original 22 and is inputted to the line sensor.
In the reduction-optical-system-type image reading apparatus shown in FIGS. 1 to 2B, if the fluorescent lamp light source is a white light source, the image sensor needs to have a color filter and, therefore, its structure is complicated.
The contact-unity-magnification-optical-system-type image reading apparatus in FIG. 3 cannot read the image from the film original.